The field of the invention is systems and methods for magnetic resonance imaging (“MRI”). More particularly, the invention relates to systems and methods for simultaneous multislice (“SMS”) imaging, in which k-space data is simultaneously acquired from multiple different slice locations.
MRI allows for the non-invasive investigation of tissues with detailed soft tissue contrast; however, it is an inherently slow imaging modality that collects data in the Fourier transform representation of the scanned object. Two-dimensional MRI involves the acquisition of multiple slices within a region-of-interest, wherein the total imaging time is proportional the number of slices that are prescribed.
SMS imaging is a technique that aims to address this shortcoming by exciting and acquiring multiple slices at once using a multichannel radio frequency (“RF”) receiver array. The multiple excited slices are then separated by exploiting the information provided by the multichannel receive arrays. Each of these receivers is sensitive to a specific region in space, and the spatial difference across the sensitivity profiles of the excited slices provides the ability to distinguish the individual slices from the acquired data. As the sensitivity of the receivers across these slices become more distinct, the capability of parallel imaging algorithms to separate these collapsed data increases.
The recently proposed blipped-CAIPI technique, described in U.S. Pat. No. 8,405,395, improves the orthogonality of the receive profiles by introducing spatial shifts across the collapsed slices. This involves exciting the slices with special RF pulses that deposit alternating phase to their Fourier transform. As a phase ramp in the Fourier representation of a signal corresponds a shift in the spatial domain, these pulses effectively create inter-slice shifts that improve the reconstruction quality of SMS imaging.
It would therefore be desirable to provide a method for simultaneous, multislice imaging that significantly decreases the amount of time required for acquiring image data; that is applicable to imaging pulse sequences that sample multiple lines of k-space following each RF excitation, such as EPI sequences; and that allows more reliable separation of aliased pixels than currently available methods for simultaneous multislice imaging, so that the benefits associated with these techniques can be realized in a clinical setting.